Crash sensors for determining that a vehicle is in a crash of sufficient magnitude as to require the deployment of an inflatable restraint system, or air bag, are either mounted in a portion of the front of the vehicle which has crushed by the time that sensor triggering is required, the crush zone, or elsewhere such as the passenger compartment, the non-crush zone. This invention is concerned with crush zone mounted sensors.
The ball-in-tube crush zone crash sensor, such as disclosed in U.S. Pat. Nos. 4,974,350; 4,198,864; 4,284,863; 4,329,549; 4,573,706 and 4,900,880 to D. S. Breed, has achieved the widest use while other technologies, including magnetically damped sensors as disclosed in U.S. Pat. No. 4,933,515 to Behr et al and crush switch sensors such as disclosed in U.S. Pat. No. 4,995,639 to D. S. Breed, are now becoming available. All of these sensors, except for some implementations of the crush switch technology, are point sensors. That is, they require that either the intruding object or material located in front of the sensor strike the relatively small front of the sensor in order for the sensor to function properly. These sensors can be called point sensors due to the small area covered by the sensors. Some implementations of the crush switch technology, such as ribbon switches, cover a much wider area of the crush zone and are line sensors, however, it has been found that there is usually insufficient available structure at the proper location in the crush zone to mount ribbon switches.
In some accidents, material in front of point sensors is not displaced rearward in time to impact the sensor and cause timely deployment of the restraint system. In these cases the sensor may either respond to the overall crash pulse in which case air bag deployment will be late, as disclosed in U.S. Pat. No. 4,900,880, or the sensor may not trigger at all. If the sensor triggers late, the occupant may be out of position and even resting against the air bag when it deploys. In this case the occupant can be killed or seriously injured by the air bag deployment, as discussed in SAE Paper 826047 "Responses of Animals Exposed to Deployment of Various Passenger Inflatable Restraint System Concepts for a Variety of Collision Severities and Animal Positions", by H. J. Mertz et al.
In many point sensor implementations, the sensor is mounted higher than the bumper so that the material in front of the sensor above the bumper must be impacted during the crash in order to cause the sensor to deploy in a timely manner. Although these sensors work well in under-ride accidents where the bumper of the vehicle rides under the object being struck, many accidents do not result in a direct impact with the material in front of the sensor. Some accidents, such as impacts with guard rails, only involve direct impact with the bumper and other accidents, called "bumper over-ride" accidents, involve impacts with the vehicle below the bumper. Although these are common, accounting for about 2% of real world accidents, present day crush zone sensor systems can fail to sense these accidents in time.
The "crush zone" of a vehicle can be defined, for the purpose of this invention description, to include that portion of the front of the vehicle which has crushed up to the time that sensor triggering is required. In a frontal barrier impact, the material in the crush zone has substantially stopped while the material in the non-crush zone is continuing to move at nearly the pre-crash velocity.
The required sensor triggering time is frequently determined to be 30 milliseconds prior to the time that an unrestrained occupant has moved a total of 5 inches (about 0.128 m.) relative to the passenger compartment. By this definition, it can be seen that the crush zone will vary from crash to crash and from one part of the front of the vehicle to another. The crush zone in a frontal barrier crash might stretch 10 inches (about 0.26 m.) back from the front-most point of the bumper for a location above the bumper, while it might stretch 13.5 inches (about 0.3 ml) back for a location directly behind the bumper. This is because, at the time that sensor triggering is required, the bumper may have a crushed thickness of 4 inches (about 0.1 m.) while the material above the bumper, such as the grill, may have a thickness of only 0.5 inches. On the other hand, for a bumper under-ride crash where the required sensor triggering time is considerably later, the crush zone above the bumper might be 13 or more inches back.
An approximate surface can be defined by subjecting a group of identical vehicles to a series of 10 MPH (about 17 kilometers per hour) crashes, for example, at different angles and different vertical engagements with the vehicle. These crashes would include fixed barriers placed at a variety of angles from -45.degree. to +45.degree. and at different elevations so that sometimes the impact is only below the bumper (bumper over-rides), at others only at the bumper, and at still others only above the bumper (bumper under-rides). Assuming that 10 MPH was the marginal velocity at which deployment of a passive restraint was desired, this 10 MPH (about 17 kilometers per hour) crush zone boundary surface would define the location for mounting of crush switch crash sensors. It would also form the location of the most rearward mounting positions for velocity change crash sensors. In practice, velocity change sensors are almost always mounted at the boundary determined by full frontal barrier impacts only.
Because of the thickness of the bumper, the 10 MPH (about 17 kilometers per hour) zone boundary is usually several inches further rearward for locations in line with the bumper than for other locations for full frontal barrier impacts. Point sensors, which are usually mounted above the bumper so that they will catch under-ride crashes, must project several inches further forward than they would if they were able to sense the rearward motion of the bumper. In many cases this results in the sensors projecting forward of the radiator into the open space behind the grill leaving them vulnerable to being rotated or damaged by maintenance or through wear and tear on the vehicle over its life.